1. Technical Field of the Invention
The present invention relates to a ground fault detector.
2. Related Art
For example, Japanese registered patent No. 4,017,770 teaches an electric leakage detector. This detector decides an electric leakage exists or not on the basis of calculating a resistance component from an electric leakage admittance and compensation of a capacitance component of a vehicle' body. The detecting method relies on a highly secure alternating current. Specifically the electric leakage detector calculates a real part of the electric leakage admittance, i.e. a resistance component, and then compares the resistance component to a certain threshold corresponds to a criterion for the leakage of electricity.
Still, Japanese registered patent No. 4,122,858 teaches another electric leakage detector. This detector detects the location of an electric leakage. More specifically the device includes multiple electric leakage detecting circuits and each circuit is respectively connected to certain portions, e.g. an inverter, through a relay. This electric leakage detector detects in which line(s) leakage of electricity occurs by means of providing separate electric leakage detecting circuits.
However, the method based on Japanese registered patent No. 4,017,770 has such a problem that the detector needs a circuit for detecting a phase difference in order to detect the admittance component. Thus the detector becomes complicated.
Though both a high-tension power supply system and a high-tension device like an inverter are commonly connected to each other by a relay, a capacitance of a common mode capacitor may be altered significantly by the relay being switched ON or OFF. The capacitance of a common mode capacitor herein means an actual capacitance of devices in the vehicle and/or its stray capacitance. Therefore the degree of the ground fault may be altered by the relay being switched ON or OFF. If the magnitude of capacitance of the common mode capacitor is larger, the amount of change of the capacitance of the common mode capacitor by the relay being switched ON or OFF may become larger. Accordingly, the user actually cannot find a location of a ground fault exactly as disclosed in Japanese registered patent No. 4,122,858.
Therefore, in the light of conditions set forth above, it is needed to provide such a ground fault detector which does not need complicated circuitry and can detect the ground fault with high accuracy in conformity to the capacitance of the common mode capacitor.